The invention relates to a magnetic transducer having poles defining a transducing gap and a multiple leg back core contiguous with the poles, and particularly to an improved core supporting structure, for use in magnetic recording/reproducing applications requiring zero spacing between the back core legs.
Magnetic transducers with multiple legs are known, for example, from the U.S. Pat. No. 3,881,194, assigned to Ampex Corporation, assignee of this patent application. The patent describes a transducer which may be utilized for recording or playback and which may be electromagnetically switched for use in one of these operating modes.
In that prior art transducer pole pieces defining a transducing gap are attached to a multiple leg back core. Each leg defines a separate flux path. One embodiment described in the patent has two back core legs, one for recording and the other one for playback. The patent discloses electromagnetic means for preventing flow of magnetic flux through that leg which is not in use during a particular selected operating mode. However, the above-indicated patent does not describe a structure for supporting the multiple leg transducer core.
It is well known that for obtaining an efficient magnetic transducer having optimum recording and reproducing characteristics, it is necessary to provide a precisely defined transducing gap while maintaining the reluctance of the rest of the flux path to minimum. The above features are generally obtained by providing a rigid transducer supporting structure in which the magnetic core members are pressed together to abut at the transducing gap, by applying a pressure sufficient for closing the transducing gap and maintaining it closed under both manufacturing and operational stresses. Such applied pressure is also utilized to minimize any additional gaps which may be provided for example for constructional reasons, such as a back core gap, to reduce unwanted fringing flux.
To that effect, conventional magnetic transducers are known to utilize magnetic core holders in the form of two corresponding side pieces made of nonmagnetic material into which corresponding transducer core portions are inserted. The side pieces are brought together in a confronting relationship at the transducing gap plane and clamped under mechanical pressure to force confronting end faces of the respective core portions to abut in precise registration. The assembly under pressure is known to be bonded together, for example, by epoxy resin. As it is well known in the art, during and following the bonding operation, a uniform controlled mechanical pressure is maintained to hold and force the core portions together while the resin hardens and sets. The result is an integrally joined rigid unitary transducer structure.
It has been observed that when such corresponding side pieces as described above are utilized for supporting a multiple leg transducer, undesirable gaps are formed in the transducer structure, thus reducing transducer efficiency as it will be described below.
FIG. 1 schematically represents a cross sectional view of a prior art transducer assembly 10. The transducer core has two corresponding core portions 12, 14. Each core portion 12, 14 is supported by a side piece 16, 18, respectively. The transducing gap 20 is formed between abutting end faces 24, 26 of corresponding magnetic poles 48, 52. It will be understood that the length "l" of the transducing gap is exaggerated in the drawings for illustration purposes. The core portions 12, 14 are assembled with corresponding poles 48, 52 and leg portions 28, 54 and 30, 56 in registration and with respective end faces 24, 26; 32, 34; and 36, 38; abutting. As it is well known in the art, during manufacturing of this type of transducers a controlled pressure indicated by arrows 40, 42 is applied to the corresponding side pieces 16, 18 and the respective transducer elements 12, 14, 16 and 18 are bonded together under that pressure by a suitable bonding material 90, such as epoxy resin. After the bonding process is completed, the externally applied pressure is removed. However, the core portions 12, 14 remain pressed together by the surrounding bonding material thus forming a rigid transducer structure having a well defined transducing gap, suitable to withstand operational stresses. It will be noted that the bonding material 90 has been deleted in the drawing from the inner portions of the core 12, 14 for clarity.
It has been observed that when pressing together the multiple leg core portions as indicated in FIG. 1, a wedge 50 is formed between the respective abutting end faces 24, 26; 32, 34; and 36, 38; respectively, due to the non-zero thickness "l" of the transducing gap material. Consequently, the intermediate leg portions 28, 54 remain substantially open during final assembly and thus in the resulting transducer structure due to the above-indicated wedge 50. The rear leg portions 30, 56 also remain open due to wedge 50 even though to a lesser extent since only a point contact is formed between the corresponding end faces 36, 38. For example, when intermediate leg portions 28, 54 are utilized for recording and rear leg portions 30, 56 for playback, such as described in the above-indicated U.S. Pat. No. 3,881,194, the recording leg 28, 54 will exhibit a relatively large gap while the playback leg 30, 56 will have a gap of a relatively smaller length. Consequently, the transducer efficiency will be reduced in both operating modes.
When utilizing the above-described type of multiple leg transducer structure in a multichannel transducer such as for longitudinal tape recording, the disadvantages related to insufficient closure of the respective multiple leg gaps are even more pronounced. As it is well known, in multichannel transducers it is desirable to have precisely uniform electrical characteristics of all the recording and reproducing channels, respectively. It has been found that when applying a uniform controlled pressure along the opposite sides of a multichannel transducer having a multiple leg back core, as shown in FIG. 1, the above-described wedge effects non-uniform gaps in both the recording and playback channels of the transducer, due to slight differences in physical dimensions of the respective elements forming these channels. For example, in a 16, 24 or 48-channel transducer of that type, there are significant differences between the channel-to-channel recording and reproducing characteristics, respectively, due to minute mechanical tolerances between individual channels of the transducer.
If the applied pressure is increased in an effort to obtain better closure of the unwanted gaps, a resulting excessive pressure may change the magnetic characteristics of the core or physically damage and eventually destroy the core.